CO2 off-gas streams produced by ethylene glycol plants typically contain saturated and/or unsaturated chlorinated hydrocarbons. In order for the CO2 off-gas to be used for the production of food grade products or for the production of methanol, urea, ethyl hexanol, or certain other applications, organic chlorides and hydrocarbons must be removed or substantially removed from the CO2 to meet acceptable industrial limits. For food-grade CO2, for example, hydrocarbons should be removed to below 5 ppmv (parts per million by volume).
Prior technologies for purification of such CO2 off-gas streams have included attempts such as oxidation of saturated and unsaturated hydrocarbons alone on precious metal catalysts, for example palladium (Pd) or platinum (Pt) catalysts. Prior techniques have also included conversion of hydrocarbons in the CO2 off-gas to CO2 and H2O followed by carbon dioxide vent to the atmosphere or further purification of a small stream of good grade CO2 by adsorption on carbon.
Further techniques for the purification of CO2 off-gas streams produced by ethylene glycol plants have included oxidation of saturated, unsaturated, and chlorinated hydrocarbons using a precious metal catalyst, for example platinum. Such methods have included the use of excess oxygen (i.e. a combustion process) for the oxidation of the saturated, unsaturated, and chlorinated hydrocarbons. Such methods have also included condensation of pure saturated water, removal of hydrogen chloride (HCl) on an adsorbent, and subsequent final removal of oxygen (O2) by reaction with hydrogen (H2) in the presence of a catalyst. Thereafter, chloride in the form of HCl is separated by absorption.
There remains a need, however, for more efficient and improved systems for the purification of carbon dioxide (CO2) off-gas streams such as those produced in ethylene glycol plants.